Low Voltage Differential Signaling (LVDS) is ubiquitous in the art. The popularity of this signaling technique arose in part from the expectation of substantially reduced power consumption because of the low (˜400 mV) swing on the lines as well as the differential nature of the signals that enabled accurate recognition despite static or dynamic variations in ground or supply voltages between the transmitting and receiving systems. Low signal swing also permits faster signal transitions, enabling higher rates of data transmission. Additionally, the differential and low-swing nature of signals also minimizes electromagnetic interference (EMI) and emissions from the signaling interconnect. Hence LVDS became the signaling method of choice for relatively long links such as high-speed links between peripheral components of a computing system (USB), networking interconnect infrastructure installed in buildings (Ethernet) etc.
Whereas the low voltage swing of 400 mV does lead to savings in power, this is not entirely beneficial because of circuit overhead, particularly at low data rates, or when interconnect is very long or lossy at the required transmission data rate. For example, to bring about a 400 mV swing across a typical 100 Ohm termination, a current of 4 mA is required through the differential interconnect pair, and in order to be able to provide such a current, typical circuits employed for LVDS communication need to operate with static currents substantially higher than this signal current requirement. This is because typical LVDS driver circuits are very similar to simple differential amplifier stages that comprise of two current-steering devices operating from a fixed current source. In combination with terminating impedances at the transmit-end to minimize signal integrity issues, a minimum of 4 times the 4 mA current, or 16 mA needs to be used as the static current source biasing the differential current-steering driver. This is akin to the 25% or lower efficiency of Class-A electronic amplifiers.
Similarly, interconnect link loss increases greatly as the data rate increases or the length of the interconnect increases. As losses increase, the available signal amplitude at the far end of the transmission link is reduced correspondingly. At multiple Giga-bits-per-second (Gbps) data rates, losses along cables may be as high as 1 dB/m, and over a 30 m length of cable as may be desired for certain multi-media or other high-data-bandwidth applications, signals may be attenuated by a factor of 31.6 or more. This would amount of signal amplitude of about 12.5 mV at the far end for a transmitted signal amplitude of 400 mV, greatly stressing the capability of receiver amplifiers in discriminating this signal from noise. Additionally, inter-symbol-interference (ISI) due to the dispersive nature of lossy interconnect degrades signal symbols further, making them indistinguishable. In such instances, therefore, low swing signals are not advantageous, and a technique for high signal swing that retains advantages of differential signaling is desired. This is also particularly true of transceiver-to-transceiver signaling link implementations where termination impedances at both ends of the link further attenuate signals, and also in instances where passive equalization techniques are employed resulting in additional signal attenuation.